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How is it possible skinny legs more powerful than muscular legs

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Jul 15, 2010
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Tapeworm said:
Incorrect. Given that cranks are fixed to each other (unless you are using powercranks or the like) the weight of the leg on one side balances the other leg. Almost the prefect counterweight*, ie: all the power driving the crank is driving the crank unless you are actively pushing on the upstroke (which usually does not happen). There is no "lifting" of the opposite leg.
You're kidding right?

The mass of the legs must be moved no matter the counterweight. I'm not going to give you a physics lesson but you even fail to take gravity into account. The weight of the legs make as much difference to the equation as the weight of the wheels and every other moving part. The most basic rules of physics dictate that the energy required to move an .... you know what, I'm not even going to bother giving you the math, I suspect you're an art student with a comment like that. Sheesh.
 
Mar 12, 2009
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Hangdog98 said:
You're kidding right?

The mass of the legs must be moved no matter the counterweight. I'm not going to give you a physics lesson but you even fail to take gravity into account. The weight of the legs make as much difference to the equation as the weight of the wheels and every other moving part. The most basic rules of physics dictate that the energy required to move an .... you know what, I'm not even going to bother giving you the math, I suspect you're an art student with a comment like that. Sheesh.
No, no please give us the math, I'd really want to see the massive differences in force between, say a cyclist with legs weighing 10kgs each and a cyclist legs weighing 20kgs each. Assume a cadence of 80rpm and a crank of 175mm.


(This has been done with the whole "weight of the wheels" thing.)

EDIT: And to be clear I am not talking about the entire mass of the complete system (ie: rider, frame, wheels etc). Total mass is total mass.
 
The whole principle of a counterweight is that work done in lifting a mass is done by the descending mass. Ordinarily I can't lift a ton of concrete but if I connect it to another ton of concrete and suspend it over a good quality pulley I will find I can lift it quite easily. So I think it's fair enough to say that the crank connects the two legs together and that the descending leg is lifting the ascending leg, (provided the ascending leg allows itself to be lifted). As such the weight of the legs would be immaterial as they cancel each out.

However, I don't believe this would apply to the situation where an uplifting force is also applied to the ascending pedal (ie pedals pulled up and pushed down simultaneously) as might be done more in sprints, accelerations and hills or by virtue of technique.

So perhaps as someone else suggested it's not a complete counterweight situation and the weight of the legs might become a factor over the course of a race?

Edit: But probably minor.
 
Dec 15, 2010
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I think it's a combination of things. The likes of Mark Cavendish at around 69kg is that he has a lot of power in those legs and with that power and so little weight, the power to weight ratio must be trough the roof. But look at him in the mountains, and he can't climb with the real climbers who don't have such large legs. That's most likely down to the fact that he's built like a sprinter... big legs. The big muscles in our legs require alot of blood to get pumped through them to keep them fuelled. So your cardiovascular system has to work harder. Anyone that goes to the gym and tries to squat heavy weights will tell you that you are out of breath alot more after a leg workout than an upper body workout since the legs require more work from the heart and lungs to pump blood around them.

So in conclusion, weight training to build strength and lose body fat to keep the power to weight ratio in your favour.
 
Jun 16, 2009
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Tapeworm said:
Incorrect. Given that cranks are fixed to each other (unless you are using powercranks or the like) the weight of the leg on one side balances the other leg. Almost the prefect counterweight*, ie: all the power driving the crank is driving the crank unless you are actively pushing on the upstroke (which usually does not happen). There is no "lifting" of the opposite leg.

* Not the PERFECT counterweight as everyone is asymmetrical.
The counterweight argument is more than a little flawed as its not just asymetry that applies here.

As has been said below, studies have shown that almost nobody produces POSITIVE power on the upstroke - fair enough - however what you are ignoring in your comment above is that the majority of trained cyclists (ie people who have spent time under coaching and/or devoting time to their cadence) the amount of NEGATIVE power applied to the pedal in the upstroke is less than that caused by the weight of the leg alone (poor wording - don't care).

The point being is that most riders do in fact at least try to get their foot out of the way on the upstroke. This not only means that the downwards leg has to do less work to produce positive power - the upward leg is working too.

How any of this applies to differnces in leg mass when there is generally a much bigger issue related to differences in overall body size is a moot point.
 
I can't speak scientifically, in terms of the physiological mechanisms at work, however, after 25 years on the bike it has always seemed to me that there is no real relationship between leg size and being strong and fast on the bike.

It has more to do with how the heart, lungs and leg muscles simultaneously work efficiently in generating sustained power to push the pedals. Often the guys with huge, muscular legs, while they may look intimidating, don't have the efficiency between these diverse elements to matter much in the long run.

There are always exceptions, of course, but, more than anything, they would seem to confirm the rule.
 
Apr 21, 2009
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The main determinant in endurance cycling is your threshold power which is a long long way away from your strength in the gym, peak speed or peak power in a Wingate test. Having conducted a fair number of Wingate tests it seems clear that even for sprinters the higher you take the peak the lower the 30sec average power becomes.

I don't see the relevance in muscle size to fat loss when muscle is far less metabolically active at rest than other major organs in the body. All hypertrophy does is lower your power to weight and increase your frontal surface area.

The focus of training for any event over 1000m should be raising ones threshold power.
 
CoachFergie said:
The main determinant in endurance cycling is your threshold power which is a long long way away from your strength in the gym, peak speed or peak power in a Wingate test. Having conducted a fair number of Wingate tests it seems clear that even for sprinters the higher you take the peak the lower the 30sec average power becomes.

I don't see the relevance in muscle size to fat loss when muscle is far less metabolically active at rest than other major organs in the body. All hypertrophy does is lower your power to weight and increase your frontal surface area.

The focus of training for any event over 1000m should be raising ones threshold power.
Yet so many races are won in a sprint. If you don't have a sprint you have a hard time winning no matter how much endurance you have. How do you improve your sprint without diminishing your threshold power?
 
Mar 12, 2009
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Not to sound pithy but... you practice sprinting more. On the road you can do all sorts of drills (starting starts, flying sprints) or practice in "race simulations".

You can have a good (road) sprint power and keep your threshold power. But you will never maximise sprint power whilst being a roadie. Specificity.
 
Apr 21, 2009
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Polyarmour said:
Yet so many races are won in a sprint. If you don't have a sprint you have a hard time winning no matter how much endurance you have. How do you improve your sprint without diminishing your threshold power?
But you do not sprint at the same power at the end of a road race or criterium at the same power you would in a match sprint.

I have the power data from a World Track Champion that looks something like this....

Peak Power 1700 watts
Peak Power in a 1000m TT: 1500watts
Peak Power in a 4000m TT: 1050watts
Peak Power in a Criterium: 1010watts
Peak Power in a 100mile Road Race: 980watts

This rider has been a NZ champion in every event from 1000m TT to the road race and has won shorter stage races and ridden Professional in the US and his results indicate that in longer events he doesn't come close to using his maximal power.

If anything from 2004 when he was recording his peak powers his average power has dropped across the board but he now races smarter and went on to win a World Track Title and has placed in several more World Cups.

Which hints to one of the ways to win more sprints beyond increasing peak power is to improve technical skills, mental toughness and race tactics.
 
Jun 16, 2009
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Polyarmour said:
Yet so many races are won in a sprint. If you don't have a sprint you have a hard time winning no matter how much endurance you have. How do you improve your sprint without diminishing your threshold power?

and if you dont have the endurance, you won't be there at the sprint anyway.

The winner of an endurance sprint is generally the rider with the best ability to produce high end watts at the end of a long day in the saddle. Part of the way they do that is to be as efficient as possible all day and if possible to protect themselves from spending any energy.

Skinny riders are able to do this and hit the required 900W or whatever. Being able to hit 2000W does nothing for you if you cant sustain the 300-400 needed to get there.
 
Sep 23, 2010
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Hangdog98 said:
You're kidding right?

The mass of the legs must be moved no matter the counterweight. I'm not going to give you a physics lesson but you even fail to take gravity into account. The weight of the legs make as much difference to the equation as the weight of the wheels and every other moving part. The most basic rules of physics dictate that the energy required to move an .... you know what, I'm not even going to bother giving you the math, I suspect you're an art student with a comment like that. Sheesh.
You are completely right, of course. The error that those that think that pedaling costs no energy is they think that because the legs are connected by the connected cranks that energy is transferred back and forth and there is no net energy cost to making the pedals go around. This is only true for the feet because they are the only part of the leg actually moving in a perfect circle so the cranks/feet behave as a spinning disk. But, the lower leg moves in an oval and the upper leg moves in a recriprocating motion. So, while the total energy of the feet is constant (meaning it takes no external energy to keep them going), the total energy of the lower legs and, especially, the thighs, is constantly changing. This requires energy input when the energy is increasing and energy loss when it is decreasing. Since the legs are not springs that can store and release this energy variation, it is an inefficiency. The amount of this energy cost depends upon the geometry (crank length, leg lengths, mass distribution, etc.) involved and the cadence. As you pointed out, the energy cost varies with the square of the cadence.

What is most amazing to me is that some of the more well respected and vocal members of these cycling forums will use as their "proof" that pedaling doesn't cost energy a model that prohibits energy loss (the rigid man model).

Anyhow, it is nice to see someone else around here who actually understands some of this stuff.
 
Sep 23, 2010
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Tapeworm said:
Uh huh.

You're all over it frank. Had to troll the forum for a while to find that post eh?
Well, I can understand your concern since you were one to call his analysis incorrect. You correctly mention that the weight of the two legs almost balance each other, but this only accounts for the potential energy part of the equation. But, your analysis completely forgets the kinetic energy part of the equation. Since energy is a scalar quantity (not directional) and both thighs are accelerating and/or decelerating at the same time it is not possible for the kinetic energy in each thigh be transferred through the fixed cranks to balance each other. It is a simple, albeit tedious, analysis
 
Mar 12, 2009
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My analysis, whilst incorrect, is not totally baseless.

Care to map out for us Frank what the actual energy cost is then to move the cranks around (talking normal cranks here) with legs of different mass? We'll assume that there are no other forces other than gravity to consider.
 
Sep 23, 2010
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Tapeworm said:
My analysis, whilst incorrect, is not totally baseless.

Care to map out for us Frank what the actual energy cost is then to move the cranks around (talking normal cranks here) with legs of different mass? We'll assume that there are no other forces other than gravity to consider.
Look, one can say that the pronouncement that the sun circles around the earth is wrong but not totally baseless because you observe the sun circling the earth every day. Wrong is wrong, regardless of how you got there and regardless of how right your observations seem.

It is pretty easy if one knows the configuration of the bike and rider and the masses of the various elements. All one need do is do the integral around an entire circle for each component and add them up. Now the integral is not that easy to do per se because we don't know the formula for the speed curve (and there can be both a linear and rotational energy component, depending upon the frame of reference. But, we can break the circle down into pieces and estimate the amount. The more pieces the more tedious the calculations but the more accurate the result. Anyhow, one will find that the only component worth worrying about is the thigh as it has the largest mass and is the part that deviates most from the circular, constant speed, motion. Know the mass of each thigh, the crank length, and the cadence and the energy variation is known. One could make the argument that the energy put into the leg could be transferred to the bike but that argument fails when pedaling unloaded. While it is possible to recover some of the energy put into the leg by transferring it to the bike when under load, it is not possible to transfer all of it because of the force directions involved (the thigh is moving up and down when it is slowing and at this time the pedal is moving mostly forward and aft). Anyhow, what is shown, if you do the analysis is this energy variation (and hence the cost of just making the pedal go around) varies with the square of the cadence. This means the power loss varies with the cube of the cadence.
 
Sep 23, 2010
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Tapeworm said:
So what I get from that Frank is you don't actually know.

Give me some figures.
Well, it depends upon the masses but as I remember (it has been awhile since I did this calculation) but as one gets up to higher cadences (90-110) the power cost can be around 100 watts. An easy way to estimate the cost to you would be to put the bike on a trainer and take off the chain. Then pedal at various cadences unloaded and see where the HR stabilizes. This should give you a reasonable idea of the oxygen cost for any cadence for you. From this you can get a good estimate of the power loss to you at any given cadence and why if you lower the cadence some efficiency tends to increase and you might actually be able to get more power to the wheel. If you graph your own data I think you will find the HR vs cadence curve is an exponential.
 
Mar 12, 2009
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So in your example, which is very light in terms of figures and formulae, of 100 watts at 100rpm, let's increase the mass if the legs by 2kgs (1 per leg). What is the cost now?
 
Sep 23, 2010
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Tapeworm said:
So in your example, which is very light in terms of figures and formulae, of 100 watts at 100rpm, let's increase the mass if the legs by 2kgs (1 per leg). What is the cost now?
That is easy. If the original mass of the legs was 10 kg per leg and the mass is distributed equally as before then the work will increase 10%, so it will cost the rider 110 watts. The cost varies directly with the mass. But, if you didn't increase the mass and increased the RPM to 140, the cost would increase 1.4^3 or to 275 watts. If the increased mass leg increased the rpm to 140 then the cost would be over 300 watts.
 
Mar 19, 2009
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CoachFergie said:
But you do not sprint at the same power at the end of a road race or criterium at the same power you would in a match sprint.

I have the power data from a World Track Champion that looks something like this....

Peak Power 1700 watts
Peak Power in a 1000m TT: 1500watts
Peak Power in a 4000m TT: 1050watts
Peak Power in a Criterium: 1010watts
Peak Power in a 100mile Road Race: 980watts

This rider has been a NZ champion in every event from 1000m TT to the road race and has won shorter stage races and ridden Professional in the US and his results indicate that in longer events he doesn't come close to using his maximal power.

If anything from 2004 when he was recording his peak powers his average power has dropped across the board but he now races smarter and went on to win a World Track Title and has placed in several more World Cups.

Which hints to one of the ways to win more sprints beyond increasing peak power is to improve technical skills, mental toughness and race tactics.
if i remember right there was a great interview with Stuart O'Grady that has stuck in my head - it's not the energy you use in a race but the energy you save.

it's why we now have 'super domestiques' who in some teams are paid more than the GC rider of rival teams.
 
Tapeworm said:
And just to further highlight the point of how the size makes little difference to the power:-

The Stick Man, Bradley Wiggins
and Brad's a "toer" (ie; rides slightly toe down) which means he uses less calf muscle and his power comes from his quads more. Toers all tend to have thin calves, yet still perform exceptionally well...
 
Mar 22, 2011
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Archibald said:
and Brad's a "toer" (ie; rides slightly toe down) which means he uses less calf muscle and his power comes from his quads more. Toers all tend to have thin calves, yet still perform exceptionally well...
Toe down results in contraction of the calf muscle and therefore more calf muscle use.
 
Sep 23, 2010
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Archibald said:
really? how much are you able to use it when it's already contracted? It means more work for the quads as the driver muscle group...
It is an interesting problem. The leg is a chain of muscles in series and it cannot push any harder than the weakest one in the chain. And, muscles are generally stronger when in isometric (not moving) contraction than when having to actually contract. And, how hard the calf must contract also depends upon where the cleat is located because of leverage. So, we can choose to "fix" the ankle with the calf muscle (the weak link in the chain compared to the quads and glutes and the only joint that can be rigid while cycling) to make it stronger but this means the other muscles must contract further, costing more energy since they are such big muscles (I am guessing). Anyhow, from a theoretical basis I cannot see any obvious advantage one way or another to any of these techniques (toes down fixed, toes flat fixed, ankling, something in between)
 

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